U.S. Pat. No. 7,180,826, U.S. Patent Publication US2008/0179093A1 and pending U.S. patent application Ser. No. 12/004,121 are herein fully incorporated by reference as describing a flow throttling device (FTD) for use in signaling applications using pressure pulses in a constrained, moving fluid column. The FTD uses hydraulic power from the moving drilling fluid to actuate the FTD against the moving fluid column. A fraction of the drilling fluid is utilized in a pilot valve to control the FTD, resulting in greatly reduced energy required to operate the FTD.
The FTD is a fast acting, high pressure, dynamic modulating valve. As such, the instantaneous forces on the mechanism are stressful. The FTD has a large operating range from several pounds to thousands of pounds of pressure drop. It is able to actuate in milliseconds, and modulate the pressure accurately. These features place a high demand on the seals which must have both low friction for the low pressure operating range, and high strength for the high pressure sealing requirements. Two pairs of seals are used. Outer seals exclude the large particulates. Inner seals support the high pressure operation.
Generally the seals used in FTDs or FMDs are of a single seal design where the seal moves bi-directionally in conjunction with the fluid flow. When the FTD or FMD is used in “clean” fluids, that is fluids containing particulates much smaller than the clearance tolerances of all moving surfaces of the FTD, the operation works in an exemplary fashion.
However, many drilling operations do not have the benefits of “clean” fluids in which to operate. Operations that employ the use of “dirty” fluids which by definition can carry aggregate particles larger or smaller than the tolerance of the moving parts. This includes moving seals, and seats, that contain particulates which contaminate the FTD or FMD actuator from moving along the full travel distance (leaking and not opening fully) or from moving at all (jamming in one of three positions; open, closed, or intermediate).
As FTD or FMD seals are in the process of seating in the presence of dirty fluids, pressure is applied to both sides of the seal area while the seal is moving. This allows for particulates to become trapped in the seal contact area which pushes the particulates together thereby contaminating the seals and contact areas. The compacting action of the moving parts on the “dirty fluid” squeezes the fluid out from the moving parts causing the particulates to wedge across the seal contact area and eventually particulates form a solid ring between the seal and the surface that subsequently jams the FTD or FMD components in both directions.
The lack of proper sealing of the FTD or FMD chambers in the presence of the “dirty fluid” diminishes the clarity of the signal and reliability of the effected seals and contact areas. The present disclosure describes a hydraulically actuated servo valve operating with pressure on both sides of the actuator and a sealing system that allows for reliable bi-directional operation in the presence of “dirty fluid” and is different from other seal applications. The present invention also defines a hydraulically amplified servo valve allowing for pressure to act on both an upper and lower side of the actuator, which has been a key problem that has been overcome with the use of this seal system design and is different than other seal applications of this type.